This application claims the priority of German patent document 100 10 532.7, filed Mar. 3, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for detecting an object using capacitive detector elements.
Capacitive object detection processes are disclosed, for example, in International Patent Document WO 99/59003 A and German Patent Document DE 19612626 A. In principle, two capacitors (usually plate shaped) are arranged adjacent to the object that is to be detected. For detecting whether or not a vehicle seat is occupied, the capacitors are situated in the upholstery, for example, in the seating and in the backrest. In this case, the detection is used for triggering safety devices, such as air bags or the like, only when the seat is, in fact, occupied.
When a person is present, the capacitance of the capacitors changes because of a human being""s relatively good conducting capacity. To differentiate between a person and a child seat, the capacitance values must be observed and be evaluated by means of an algorithm.
It is an object of the present invention to provide a process of the initially mentioned type which, with low equipment expenditures, supplies precise information concerning not only the presence of an object but also about which object is involved.
This and other objects and advantages are achieved by the detection process according to the invention, capacitors arranged in the backrest and in the seat surface are influenced by an object. The capacitors are acted upon by alternating voltage, and the time variation of their capacitances is determined individually.
In a first process according to the invention, two evaluations are derived by means of a value table and are compared with one another. If the two evaluations correspond with respect to the type of the object, the safety device is controlled as required (that is, triggered; or for example in the case of a rebound child seat or in the case of an unoccupied seat, it is not triggered).
In the second process according to the invention, the two evaluations are mathematically related to one another, and based on the value resulting from the mathematical relationship, a decision table is used to determine whether, as required, an occupant protection device assigned to the seat is activated. The mathematical relationship can preferably be an averaging or an adding of the two evaluations. Only an overall evaluation is used here.
It is important for both processes that the variation in time of the capacitances, and thus the information concerning the type of the object, is followed. Thus, the result of the decision as to whether, as required, the occupant protection system should be activated can also be examined with respect to its variation in time.
Finally, the decision to activate the occupant protection system as required can be annulled only after a set time has expired during which a decision is constantly present which prevents the activation of the occupant protection system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.